Comparative study on the geochemical characteristics of rare earth elements in deep-sea sediments from different regions of the Pacific Ocean

The deep-sea sediments in the Pacific Ocean are rich in rare earth elements (SREE+Y: SREY) which is considered to be a potential new resource of the rare earth elements. Zeolite clay, pelagic clay and polymetallic mud are the main types of sediments rich in REY. The zeolite clay and pelagic clay are mainly distributed in the central and northwestern Pacific basin, while polymetallic mud is mostly distributed in the deep-sea basin near the eastern Pacific ridge. At present, there are many researches on the pelagic clay and zeolite clay in the central and northwestern Pacific, but less on the polymetallic mud. What are the differences of REY occurrence in different regions and different types of sediments? The influence factors of the enrichment of REY in the deep-sea sediments are still unclear. All these further affect the exploration and development of REY resources in deep-sea sediments. The geochemical and mineralogical characteristics of different types of deep-sea sediments in different regions of the Pacific Ocean are analyzed and compared. The results show that the REY contents in deep-sea sediments in the central and northwestern pacific, especially in zeolite clay, are generally significantly higher than those in the eastern Pacific polymetallic mud. The REY contents in zeolite clay and pelagic clay are mainly related to phosphate. The CaO/P2O5 ratios in supernormal high REY (Sigma REY>2000x10-6) sediments (similar to 1.4) tend to be consistent and almost close to CaO/P2O5 ratios of the apatite (similar to 1.3). Therefore, apatite is the main carrier and enrichment of REY in deep-sea sediments in this area may be affected by phosphorylation. The polymetallic muds with high contents of Fe and Mn are affected by obvious hydrothermal activities. However, the SREY content of the mud are mainly within the range of 500x10(-6)similar to 800x10(-6), which do not change with the increase of Fe and Mn. The enrichment of REY is still closely related to phosphate, but not with hydrothermal Fe-oxyhydroxides, Mn-oxides and aluminosilicate. The deep-sea sediments rich in REY in the central and northwestern Pacific need a strong oxidation environment and sufficient phosphorus content. However, the SREY content of the polymetallic mud is usually lower than that of the zeolite clay in the central and northwestern Pacific because of less phosphorus supply although in oxidation environment.